The present invention generally relates to monitoring, metering, protection and control of electrical systems, and more specifically, to an apparatus and method for identifying a phase associated with device terminals at a location of an electrical power system.
Knowledge of the state of an electrical power system is important in order to recognize and understand disturbances in the electrical power system, provide protection functionality, automation, metering, monitoring, and control actions associated therewith. Electrical power systems include a variety of power system elements such as circuit breakers, current transformers, voltage transformers, electrical generators, electrical motors, power transformers, power transmission lines, buses and capacitors, to name a few. Electric power systems also include various automation devices, monitoring devices, control devices, metering devices, and protective devices (e.g. protective relays, remote terminal units (RTUs), recloser controls, sectionalizer controls, meters, etc.).
In most cases, these devices are microprocessor-based or intelligent electronic devices (IEDs) that provide proper metering, monitoring and control functionality from the determination and/or processing of current and/or voltage signals from the power system. As shown in FIG. 1, modern power systems are three-phase systems wherein each phase associated with a voltage VA 102, VB 104, Vc 106 is offset from the others by about a 120° phase shift. Similarly, as shown in FIG. 2, modern power systems are three-phase systems wherein each phase associated with a current IA 202, IB 204, Ic 206 is offset from the others by about a 120° phase shift. Each phase is assigned a phase designation, typically A, B and C. The correct and proper execution of monitoring, control, automation, metering and protective devices is dependent on the proper identification of the phase associated with each device current or voltage terminal connected to the electrical power system.
Nevertheless, phase identification is often difficult to ascertain for certain locations in the power system. In one example, a recloser is a device including a mechanism for controlling a circuit breaker associated with a location in the power system. Reclosers are typically used in coordinated protection schemes for overhead power lines. For example, when a fault is detected at a location on the power line, a protective device such as a protective relay or recloser control would open a circuit breaker or recloser associated therewith to isolate the fault from the remainder of the power system. Were the fault is temporary, the protective relay or recloser control would issue an automatic reclose command to the circuit breaker or recloser to resume normal operation. When the fault is permanent, the protective relay or recloser control goes through a preset open-close-open sequence to lock out the circuit. After the fault is cleared, the protective relay or recloser control would be used to close the circuit breaker or recloser to resume normal operation.
Reclosers require a proper connection to a three-phase power system. Accordingly, reclosers require the proper identification of the phase associated with each of its current or voltage terminals connected to the electrical power system. Such phase identification proves difficult as the recloser can require six voltage connections and three current connections at a location on the power system. For example, in FIG. 3, at a location in a power system 300, a recloser control 302 (e.g., protective relay) is associated with a power system apparatus 304 (e.g., recloser or circuit breaker). For proper control of the power system apparatus 304, the recloser control 302 requires a proper identification and three-phase voltage connection at the source (VST1, VST2, VST3), a proper identification and three-phase voltage connection at the load (VLT1, VLT2, VLT3), and a proper identification and three-phase current connection at the load (CT1, CT2, CT3).
Accordingly, it is an aspect of the present invention to provide a method power system for identifying a phase associated with device terminals at a location of an electrical power system.